1. Field of the Invention
This invention relates to a magnetoresistance effect type head to be used as a reproducing head for a magnetic recording and a separate recording-reproducing type magnetic head using the magnetoresistance effect head.
2. Description of the Related Art
In recent years, high densification of magnetic recording has advanced to the extent of realizing systems of such high levels of recording density as 500 Mb/inch2 in VTR and 200 Mb/inch2 in HDD for practical use. The demand for further densification of magnetic recording is -steadily increasing in enthusiasm. This trend of the magnetic recording toward higher densification entails the essential task of reducing track width. In the case of a 200 Mb/inch2 HDD system, for example, a track width is 7 xcexcm and the track-to-track separation is about 2 xcexcm and, therefore, the tolerance of the track width is roughly the distance (2 xcexcm) between the adjacent loops of the track. For the sake of attaining further exaltation of the recording density, it is necessary that the track width should be reduced to below 5 to 6 xcexcm and the tolerance should not be more than 0.5 xcexcm. In order to exalt the density of recording to the level of about 10 Gbits/inch2, it is expected that the track width would be required to be not more than 1 xcexcm and the tolerance thereof to be roughly 0.1 xcexcm. For the purpose of fulfilling these requirements, the magnetic head requires a marked improvement.
A method for defining such a narrow track-width of heads has been reported, by which magnetic core in air bearing surface is focused ion etched (refer to Japanese Patent Laid-Open Application No. 3-296907). This method, however, is handicapped greatly in the capacity for mass production because the method requires processing of the magnetic heads one by one and the focused ion beam etching technique itself has a very poor throughput, though the method is capable of infallibly producing an accurate track width.
A thin-film magnetic head has been reported (Japanese Patent Laid-Open Application No. 3-205607) which has a magnetic core on the air bearing surface the width of which increases in proportion to the distance from the magnetic gap. This method, however, is incapable of acquiring ample forming accuracy because it requires to impart diverging cross sections to the magnetic cores. It is further disadvantageous that it incurs difficulty during the impartation of an axis of easy magnetization in the direction of track width to the narrowed track and fails to confer ample high-frequency permeability on the track.
As respects the reproducing head for a system of such a high recording density as mentioned above, the magnetoresistance effect type head (hereinafter referred to as xe2x80x9cMR headxe2x80x9d) which utilizes magnetoresistance effect, the phenomenon that the electric resistance of a certain type of magnetic thin film or magnetic multilayer thin film is varied by an external magnetic field, has come to attract attention. Since the MR head is capable of producing a high output even in a system having a low relative speed between a head and a medium, it has been heretofore used mainly in stationary head type tape medium reproducing systems. Since the MR head possesses a high S/N, however, it has come to be adopted recently even for the small HDD which has such a low relative speed as several meters/second in the place of the induction type reproducing head.
FIG. 27 shows one example of the construction of the conventional shield type MR head. A pair of leads 2 are connected severally to the opposite ends of a magnetoresistance effect film 1 made of an anisotropic magnetoresistance effect film, a spin valve film, or a artificial lattice film. They jointly form a magnetoresistance effect element (hereinafter referred to as xe2x80x9cMR elementxe2x80x9d) 3. This MR element 3 is placed between insulating films 4 and 5 which form a reproducing magnetic gap. On the outer sides of the insulating films 4 and 5, a pair of upper and lower shield layers 6 and 7 capable of defining linear resolution are respectively disposed. The upper shield layer 7 concurrently serves normally as a lower magnetic core of the magnetic head. On the upper shield layer 7, an upper magnetic core 9 is formed through the medium of an insulating film 8 which forms a recording magnetic gap. These components jointly form a recording magnetic path. When the shield type MR head constructed as described above is used as a reproducing head, the linear resolution thereof is substantially determined by the length of the upper reproducing magnetic gap (the thickness of the insulating film 5) or the length of the lower reproducing magnetic gap (the thickness of the insulating film 4). In the construction of the conventional MR head, however, for the sake of securing insulation between the lead 2 and the upper shield layer 7, it has been necessary that the insulating film 5 should be formed in a thickness roughly equal to step height of the lead. As a result, it has been extremely difficult to define the high linear resolution to a level of not more than the thickness of the lead 2. In fact, the thickness of the lead 2 is desired to be not less than 0.2 xcexcm for the purpose of enabling the MR element to keep its ratio of change of resistance. Thus, the improvement of the linear resolution to be attained in the shield type MR head has had its own limit.
In the system of such high recording density as a recording density exceeding the order of Gb/inch2, for example, since the necessary linear resolution is equal to or smaller than the thickness of the lead of the shield type MR head, the shield type MR head of the conventional construction described above is incapable of attaining this high linear resolution. Under the circumstances, the desirability of realizing a shield type MR head possessing such a high linear resolution as is suitable for a system of high recording density exceeding the order of Gb/inch2 has been finding growing recognition.
Further, in the case of a recording density of 1 Gb/inch2, for example, the width of the shield layers 6 and 7 is desirably set at a level in the approximate range of from 3 to 5 xcexcm because the track width is about 3 xcexcm. Since the shield layers 6 and 7 have a thickness of about 2 xcexcm, the MR element 3 must be formed on a protruding part measuring approximately 2 xcexcm in height and 3 xcexcm in width. In the case of a greater recording density of 10 Gb/inch2, it is more sternly necessary that the MR element 3 should be formed on a protruding part approximately measuring 2 xcexcm in height and 1 xcexcm in width. An attempt to restrain the size as of the track width of the MR element of a micron order on a substrate having such a protrusion as mentioned above merely results in seriously degrading the yield of production. If a resist 3 xcexcm in thickness is formed on a substrate having a protruding part roughly 2 xcexcm in height and 2 xcexcm in width and a stripe (remnant) pattern 1 xcexcm in width is formed on the resist, for example, the difference of the width of the MR pattern between on a mask and on a wafer will inevitably amount to xe2x88x920.3 xcexcm. Thus, the conventional shield type MR head entails the problem of imparting an abrupt jog to the substrate of the MR element and rendering accurate regulation of the track width of the MR element no longer practicable when an attempt is made to improve the recording density as described above. When the recording head is formed on the shield type MR head which is constructed as described above, the magnetic gap of the recording head is such that the linearity thereof depends on the thickness of the lead 2 of the MR element 3 as clearly remarked from FIG. 27. The lead 2 in this case is generally formed by the lift-off method which inflicts only slight damage to the MR element 3. The lead 2 which is formed by this lift-off method forms projections in the edge parts at a certain degree of probability even when a reversely tapered resist is used. As a result, the yield of production is degraded by the phenomenon of shortening between the leads and the shield when the projections go to narrow the gap between the shield and the lead. Indeed, the degradation of the yield by the shortening can be prevented to a certain extent by decreasing the thickness of the lead 2. The lead 2, however, does not tolerate a generous decrease of thickness because the decrease of thickness of the lead 2 results in an increase of resistance and a substantial decrease of the ratio of change of resistance.
Specifically, regarding the layout of the lead 2, the practice of disposing the lead 2 in such a manner that the area in which the shield 7 and the lead 2 overlap each other may be decreased to the fullest possible extent as shown in FIG. 28 is followed for the purpose of precluding the shortening between the shield and the lead. FIG. 29 shows the relation between the ratio of change of resistance of the MR element and the variation of the thickness of the lead 2 as determined with respect to varied track widths (TW) in the construction having the lead 2 disposed as described above. It is clearly noted from FIG. 29 that the dispersion of the specific resistance of the lead 2 increases and, as a result, the ratio of change of resistance abruptly decreases when the thickness of the lead 2 decreases below about 0.4 xcexcm. In order to keep the ratio of change of resistance from decreasing extremely, therefore, it is necessary that the thickness of the lead should be not less than about 0.4 xcexcm, and not less than about 0.2 xcexcm at least.
In the shield type MR head of the conventional construction, the linearity of the recording magnetic gap depends on the thickness of the lead as described above. If the thickness of the lead does not decrease in proportion as the length of the recording magnetic gap decreases as expected in the future, therefore, the linearity of the recording magnetic gap will be degraded more seriously by the difference of level due to the thickness of the lead. With such a track width as the maximum of 5 xcexcm, therefore, the off-track characteristic will be degraded to a great extent. As a result, a heavy azimuth loss is suffered to occur when the MR element is operated for reproduction. In actuality, the degradation of the linearity of the recording magnetic gap which occurs as described above poses a problem when the recording magnetic gap is formed in a size roughly not more than 10 times the thickness of the lead.
An object of this invention, therefore, is to provide a shield type magnetoresistance effect type head which is capable of acquiring a linear resolution suitable for a system of high recording density having a planar recording density exceeding the order of Gb/inch2, for example. A further object of this invention is to provide a shield type magnetoresistance effect type head which is capable of permitting accurate regulation of sizes such as the track width and, at the same time, acquiring a large ratio of change of resistance and, therefore, is suitable for a system of high recording density.
Another object of this invention is to provide a separate recording-reproducing type magnetic head which is adapted for such a system of high recording density as mentioned above and, at the same time, adapted to manifest exalted recording-reproducing characteristics. Yet another object of this invention is to provide a separate recording-reproducing type magnetic head which is prevented from entailing degradation of the off-track characteristic thereof in consequence of an increase of the recording density.
The first magnetoresistance effect type head of this invention is characterized by comprising a magnetoresistance effect film having a pair of leads connected thereto and possessing a magnetic field responding part, a lower shield layer disposed on the lower side of the magnetoresistance effect film through the medium of a magnetic gap forming insulating film, and an upper shield layer disposed on the upper side of the magnetoresistance effect film through the medium of another magnetic gap forming insulating film, which magnetoresistance effect type head satisfies the relations, Ws  less than Wr and Tr less than Wr, wherein Ws stands for the width of the surface of the upper shield layer facing the magnetoresistance effect film, Wr for the distance between the pair of leads, and Tr for the width of the magnetic field responding part of the magnetoresistance effect film.
The active region, which responds to a magnetic field, is formed of the remainder of the MR film region whose magnetic moment is fixed. Alternatively, the active part is formed of the protruding part of the magnetoresistance effect film extended in the direction of the surface thereof facing the medium.
The second magnetoresistance effect type head of this invention is characterized by comprising a magnetoresistance effect film having a pair of leads connected thereto and a pair of shield layers having the magnetoresistance effect film interposed therebetween through the medium of a magnetic gap-forming insulating film, at least either of the pair of shield layers being formed as embedded at least partly within a trench formed in the insulating layer.
Further the first separate recording-reproducing type magnetic head of this invention is characterized by comprising a reproducing head formed of the first magnetoresistance effect type head mentioned above having an upper shield layer so shaped as to possess a protruding part extended in the direction of the magnetic gap-forming insulating film and a recording head formed of a induction type head possessing a pair of magnetic cores opposed to each other through the medium of a magnetic gap, the lower of the pair of magnetic cores being formed of a magnetic material layer shared with the upper shield layer of the magnetoresistance effect type head and, the surface of at least either of the pair of magnetic cores facing the medium possessing a protruding part extended in the direction of the magnetic gap.
The second separate recording-reproducing type magnetic head of this invention is characterized by comprising a reproducing head formed of a magnetoresistance effect type head possessing a magnetoresistance effect film having a pair of leads connected thereto and a pair of shield layers having the magnetoresistance effect film interposed therebetween through the medium of a magnetic gap forming insulating film and a recording head formed of an induction magnetic head superposed on the magnetoresistance effect type head and possessing a pair of magnetic cores opposed to each other across a magnetic gap of a size of not more than 10 times the thickness of the lead of the magnetoresistance effect type head, the magnetic gap possessing substantial linearity throughout the entire width of the recording track.
In the first magnetoresistance effect type head, the leads are disposed outside the substantial opposite edges of the reproducing magnetic gap by causing the distance Wr between the leads to be larger than the width Ws of the surface of the upper shield layer facing the magnetoresistance effect film. Owing to this arrangement, the effect of the thickness of the leads on the length of the reproducing magnetic gap can be eliminated. As a result, the desire to decrease the gap can be realized and the linear resolution suitable for the exaltation of recording density even exceeding the order of Gb/inch2 can be attained.
Further, since the width Tr of the active region of the magnetoresistance effect film is caused to be smaller than the distance Wr between the leads and preferably smaller than the width Ws of the surface of the upper shield layer facing the magnetoresistance effect film, the cross talk possibly induced by the decrease of the track width can be precluded and the exaltation of linear resolution can be attained by the decrease of the gap as well. In short, the decrease of the gap and the decrease of the track width can be obtained without inducing degradation of the regenerating characteristics.
The first separate recording-reproducing type magnetic head enables a system of high recording density to produce desired recording and reproducing operations stably because it uses a reproducing head formed of the aforementioned first magnetoresistance effect type head and a recording head formed of an induction magnetic head. The induction magnetic head used herein allows the decrease of track width to be realized with high accuracy because the surface of the magnetic core facing the medium is so shaped as to possess a protruding part extended in the direction of the recording magnetic gap. Further, since the axis of easy magnetization of the protruding part of the magnetic core is easily aligned in the direction of the track width in this case, the axis of easy magnetization can be paralleled with the direction of the track width enough to obtain ample high-frequency permeability stably even when the track width is decreased.
In the second magnetoresistance effect type head, since at least one of the pair of shield layers is formed as embedded in a trench formed in the insulating layer, the upper surface of the shield layer is enabled to keep flatness and smoothness intact. Then the magetoresistance element or the upper magnetic core is formed on the shield layer having such a flat and smooth surface, therefore, the work for decreasing the track width can be carried out accurately and easily even when the width of the shield layer is small and, at the same time, the acquisition of ideal ratio of change of resistance can be ensured.
In the second separate recording-reproducing type magnetic head, linearity is substantially imparted to the recording magnetic gap throughout the entire width of the recording track of the induction magnetic head serving as a recording head by causing the shield layer concurrently serving as a lower magnetic core and excelling in flatness and smoothness to be formed as embedded in the trench formed in the insulating layer and having the recording magnetic gap formed on the shield layer. As a result, the off-track characteristic which is manifested during the reproduction by the magnetoresistance effect type head can be markedly improved.